Mutants of Ustilago maydis defective in production of one of two polypeptides of KP6 toxin from the preprotoxin

Jianshi Tao, Idit Ginzberg, Yigal Koltin*, Jeremy A. Bruenn

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Double-stranded RNA viruses of Ustilago maydis encode secreted killer toxins to which other cells of the same species and closely related species are sensitive. KP6 toxin consists of two polypeptides, α and β, produced from a single precursor preprotoxin. In this work, we cloned complementary DNA for the toxin-encoding segment of two of the KP6 nonkiller mutants NK3 and NK13 that secrete the β and α polypeptides, respectively. Both sequence analysis of the cDNA clones and in vitro translation of the toxin-encoding double-stranded RNAs showed that both mutants can produce full-length preprotoxins. Cys51 in α is converted to Arg in NK3 and Thr25 and Lys42 in β are changed to Pro and Arg, respectively, in NK13. Although α and β are encoded in a single prepropolypeptide, only the β polypeptide is secreted by NK3 and only the α polypeptide is secreted by NK 13. This differential expression of peptides from one precursor is a unique phenomenon. Neither of the nonsecreted polypeptides accumulated in the cytosol. The possible effects of these mutations on pre-protoxin folding and their consequences for toxin secretion are discussed.

Original languageEnglish
Pages (from-to)234-240
Number of pages7
JournalMolecular Genetics and Genomics
Issue number1-2
StatePublished - Apr 1993


  • Double-stranded RNA virus
  • Killer toxin mutants
  • Toxin conformation
  • Ustilago maydis killer toxin


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